1. Field of the Invention
The present invention relates to a system and a method with which autonomous mobile units can be moved into a parked position wherein an orientation aid is used for controlling such position.
2. Description of the Prior Art
Autonomous mobile units can be employed in office, hospital or industrial settings in order to perform simple activities such as those relating to transport, remote manipulation, or cleaning. Given the use of autonomous mobile robots of this type, it is particularly desirable for them to be able to dock in a precise manner in order to take on or deliver cargo, to perform a battery change, or to replace the cleaning device in a cleaning machine. Another instance of docking can occur when the autonomous mobile unit drives into a garage in which it waits until further requests for action are directed to it. During this wait time, for example, an accumulator that is provided in the autonomous mobile unit can be charged, or a self-diagnosis of the device can be executed.
Various methods and devices for position detection of mobile units are taught by, for example U.S. Pat Nos. 4,679,152, 4,627,511, 4,938,495, and European Patent No. EP-A-0736 630.
The device for position detection described in U.S. Pat. No. 4,938,495 is used in the framework of a coupling process of a member of a train device.
In the method taught by European Patent No. EP-A-0736 630, which is used in the framework of renewing an existing striping on a road, an angle is determined that is circumscribed by a street marking machine and the present striping.
A problem that arises in the docking of such units described in these references is that the device must be brought from an arbitrary starting configuration into a strictly defined end position. Known autonomous mobile units such as those described in the German patent P 44 21 805 orient by themselves using ultrasound sensors and by using odometry measurements that are performed at a wheel of the unit. During the device""s journey from a starting point to a target point, the configuration errors which are caused by the imprecisions of the sensor in the odometry measurements and in the ultrasound distance measurements add up, so that before long a precise orientation is no longer possible unless countermeasures are taken. In the cited patent, countermeasures are taken in that different actions to be performed by the autonomous mobile unit are evaluated, and the configuration error is monitored. If too large an error arises, corrective measures are initiated.
Another problem is that the autonomous mobile unit in a docking station should preferably dock in a very specific rotational orientation and with a very specific exterior. But autonomous mobile units of this type usually have three-wheel kinematics, which does not enable them to move forward arbitrarily on a movement underlay. The three-wheel kinematics of autonomous mobile units is discussed in the German patent 195 21 358, for example. There, the slippage that builds up along a planned travel path of such an autonomous mobile unit is additionally detected.
The present invention is therefore directed to a system and a method with which an autonomous mobile unit can be moved into a defined end position in a docking station.
Such object is achieved in a system and method wherein a good orientation aid is made available by the application of a slot-shaped light beam, which is situated perpendicular to the movement underlay of the unit, in connection with a position-sensitive detector for this light beam, which is attached parallel to the unit""s driving face, such that it is possible with such orientation aid to directly generate a signal for a drive path control of the unit for controlling the docking position.
Specifically, in an embodiment of the present invention, a system for positioning an autonomous mobile unit for docking is provided, which includes: a transmitter and a detector wherein one of the transmitter and the detector is arranged at the autonomous mobile unit and the other of the transmitter and the detector is arranged at a docking device, the transmitter emitting a slot-shaped light beam which is substantially perpendicular to a drive surface of the autonomous mobile unit, the detector including at least one position detector which is oriented substantially parallel to the drive surface for detecting a position of the light beam; and an evaluator which receives data from the detector and evaluates a change of relative position of the light beam with respect to the detector to control movement of the autonomous mobile unit wherein the light beam assumes a particular position on the position detector.
In an embodiment, the system includes means for determining a docking interval between the autonomous mobile unit and the docking device; and an actuator for activating the transmitter given a failure to exceed a first docking interval.
In an embodiment of the system, the detector includes at least two position detectors arranged one behind the other in a main direction of approach to the docking device of the autonomous mobile unit.
In an embodiment of the system, the position detector is a conventional position-sensitive detector.
In an embodiment of the system, the position detector includes photodiodes.
In an embodiment of the system, the position detector includes photo transistors.
In an embodiment of the system, the transmitter includes a laser for generating the light beam.
In an embodiment of the system, the transmitter includes both a filament lamp and a Fresnel lens for generating the light beam.
In an embodiment of the system, the actuator includes an infrared sensor.
In another embodiment of the present invention, a method for docking an autonomous mobile unit at a docking device is provided, the method including the steps of: arranging one of a transmitter and a detector at the autonomous mobile unit and the other of the transmitter and the detector at the docking device; emitting a slot-shaped light beam from the transmitter, the light beam being substantially perpendicular to a drive surface of the autonomous mobile unit; detecting a position of the light beam with at least one position detector provided in the detector, the position detector being oriented substantially parallel to the drive surface; receiving data from the detector at an evaluator; evaluating a change of relative position of the light beam with respect to the detector via the evaluator; and controlling movement of the autonomous mobile unit wherein the light beam assumes a particular position on the position detector.
In an embodiment, the method further includes the steps of: providing three-wheel kinematics for the autonomous mobile unit; determining whether it is possible for the autonomous mobile unit to attain a desired docking position based on the kinematics and depending on a docking interval; and distancing the autonomous mobile unit from the docking device, if it is determined that it is not possible for the autonomous mobile unit to attain the desired docking position, sufficiently far enough to enable the autonomous mobile unit to ultimately attain the desired docking position.
In an embodiment, the method further includes the steps of: determining, in cyclical, integral brightness differences in an environment of the autonomous mobile unit; and evaluating the brightness differences as interval changes to obstacles in the environment.
In an embodiment, the method further includes the steps of: providing at least two distance measuring sensors at a side of the autonomous mobile unit; determining a distance to a wall placed to a side of the docking device using the at least two distance measuring sensors; determining a distance to the docking device using at least one further distance measuring sensor provided at the autonomous mobile unit; determining a configuration of the autonomous mobile unit from a known distance to the docking device from the wall and from the measured distance to the wall; and forming control signals for a docking procedure based on the configuration of the autonomous mobile unit.
An advantage of the described system and method consists in its provision of means by which the light beam is activated only when the autonomous unit is approaching the docking station, wherein it is possible to save energy.
Another advantage of the described system and method is that it provides two detection means for the light beam, these being consecutively arranged in a main direction of approach of the unit, so that a more precise orientation of the unit in relation to the docking device can be achieved.
Another advantage of the described system and method is that conventional position-sensitive detectors can be employed as detection means for the light beam.
Another advantage of the described system and method is that conventional photodiodes can be used for the detection of the light beam if a low resolution is permissible or if cost considerations play a role.
It is particularly advantageous that the described system and method be equipped with a laser, which makes available a rather precise punctiform light source, thus enabling a precise orientation in relation to the docking device. This laser preferably operates in the infrared region, whereby people in the vicinity of the device are not endangered.
It is particularly advantageous for the laser to operate in the pulsed mode, since an identification code for the laser can be generated with the pulsed signal.
It is also particularly advantageous in the described system and method if triggering means for the light source are provided in the form of an infrared transmitter and receiver, since these are widely used in the form of remote controls and can be produced in a cost effective manner.
It is further advantageous if an autonomous mobile unit operates with a docking method and system in which it determines its configuration relative to the docking device with the aid of the transmitted light beam and determines, with the aid of its three-wheel kinematics, if it can purposefully attain the docking device from this configuration in order to be able to dock there. If this is not the case, it distances itself therefrom autonomously and centers itself relative to the docking device. This method has the advantage in that there is no need for information of any sort about the environment of the docking device.
It is particularly advantageous in the described docking method and system that information about the environment of the docking device can be additionally exploited such that a known distance from the docking device to a sidewall is measured by the autonomous mobile unit, and the position of the docking device is deduced. With an additional distance measuring sensor with which the distance to the docking device is measured, the exact position of the unit can be detected and the docking process can be initiated.
Additional features and advantages of the present invention are described in, and will be apparent from, the Detailed Description of the Preferred Embodiments and the Drawing.